A research scientist who believes in different states of consciousness uses a sensory deprivation tank and hallucinogenic drugs to find the ultimate truth. But soon his mind-altering experiments get out of control...

In the basement of a university medical school Dr . Jessup floats naked in total darkness. The most terrifying experiment in the history of science is out of control... and the subject is himself

Movie Quote(s):

Eddie Jessup: The purpose of our suffering is only more suffering.

Arthur Rosenberg: The way I feel, I don't expect to go to sleep for a year. I'm on fucking fire!

Eddie Jessup: What dignifies the Yogic practices is that the belief system itself is not truly religious. There is no Buddhist God per se. It is the Self, the individual Mind, that contains immortality and ultimate truth. Emily Jessup: What the hell is not religious about that? You've simply replaced God with the Original Self. Eddie Jessup: Yes, but we've localized it. Now I know where the Self is. It's in our own minds. It's a form of human energy. Our atoms are six billion years old. We've got six billion years of memory in our minds.

Eddie Jessup: Memory is energy! It doesn't disappear - it's still in there. There's a physiological pathway to our earlier consciousnesses. There has to be; and I'm telling you it's in the goddamned limbic system. Mason Parrish: You're a whacko! Eddie Jessup: What's whacko about it, Mason? I'm a man in search of his true self. How archetypically American can you get? We're all trying to fulfill ourselves, understand ourselves, get in touch with ourselves, face the reality of ourselves, explore ourselves, expand ourselves. Ever since we dispensed with God we've got nothing but ourselves to explain this meaningless horror of life.

Eddie Jessup: You saved me. You redeemed me from the pit. I was in it, Emily. I was *in* that ultimate moment of terror that is the beginning of life. It is nothing. Simple, hideous nothing. The final truth of all things is that there is no final Truth. Truth is what's transitory. It's human life that is real. I don't want to frighten you, Emily, but what I'm trying to tell you is that moment of terror is a real and living horror, living and growing within me now, and the only thing that keeps it from devouring me is you. Emily Jessup: Why don't you just come back to us? Eddie Jessup: It's too late. I don't think I can get it out of me anymore. I can't live with it. The pain is too great.

Movie Trivia:

Author Paddy Chayefsky disowned this movie. Even though the dialogue in the screenplay was almost verbatim from his novel he reportedly objected to the over the top shouting of his words by the actors.

Arthur Penn was originally slated to direct but resigned.

The book was partially based on dolphin researcher John Lilly, who invented the isolation tank, and first started taking drugs while "tanking".

Director Trademark: [Ken Russell] [snake] the dream sequence

In his autobiography, director Ken Russell said he tried mushrooms during the making of the film, which resulted in a bad trip.